18.4 - Implementation

Fabrication

The parts fabricated for our prototype and final product were primarily produced using either a laser cutter or 3D printer.

Our design consisted of horizontal and vertical base plates, which were placed perpendicular to each other. These plates would be produced from 6mm wooden boards sold by TIW using a laser cutter. After parts have been designed and assembled on the base outlines in SolidWorks to ensure proper spacing and dimensioning,  holes are placed and a .dxf drawing is generated. The .dxf drawing is then converted into a .svg and uploaded onto a laser cutter. This is the same process which was used to fabricate the acrylic shelf for the electronics.

Figures 1&2: A side by side example of the SolidWorks model (left) and the .dfx drawing generated from the model (right), this is the precursor to the finished version of the part seen in figure 9

We used additive manufacturing for many of the parts in our device due to the technology's ability to supply highly customized parts with difficult to machine dimensions at a reasonably quick pace. This would allow us to not only iterate on designs more quickly, but also to crate multiple versions of a part which could be tested against each other, thus saving time.

To produce the 3D printed parts we needed, we would design the parts in SolidWorks. We would then convert the part into an .stl and upload it onto either Bambu Studio or ideaMaker software. On the software, we would select the parts that we wanted to print, selecting various infill, print pattern, and support options, and arrange the parts with optimal spacing and orientation to ensure higher part strength, lower print times, and reduced post-processing. Once the build was ready, it would be sliced and exported as G-code. The G-code would then be uploaded to the machines and the print would be started. At the conclusion of the print, the parts would be collected and post processed by removing support and sanding rough surfaces. This process would be followed for a wide array of parts throughout or device, which will be discussed in the assembly section.

Figures 3, 4, 5, 6 (In order): These figures show the process of taking a part through the steps from SolidWorks model to STL in ideaMaker to a sliced model, which is ready be exported as G-code for the machine. The final image shows an example of the many different parts and iterations of those parts that went into the design of our device.

To adapt lengths of 8mm and 6mm rail for use in our device, we used an abrasive saw. With this type of saw, we were able to quickly and precisely cut the hardened steel rods we were using for the slider supporting the follower in our device, as well as the gear train and cylinder.

Figures 7 & 8: An example of an abrasive saw, also known as a chop saw, and lengths of 8mm shafts which have been cut to length

Assembly

The assembly of the final device could be divided into four major sections: The base, the motor and cam, the follower, and the gear train and cylinder.

The base as mentioned previously consisted of two laser cut wooden plates. The horizontal plate had two slots for fitting the vertical plate. For added stability, the plates also have holes for bolting on four 3D printed L-brackets, two per side and are offset from the table by a cut out to provide space for nuts on the bottom of the horizontal base.

Figure 9: A picture of the final assembled device, built on the frame created by the two base plates

The cam sits on a 6mm rod held up by two 3D printed bearing mounts with raisers containing 6mm ID ball bearings. This connects to the 12V 1.6A stepper motor, which is powered by a power supply and controlled by an arduino and motor driver. The power supply is held above the electronics by an acrylic shelf held off up by offsets. (An example of the electronics can be seen in figure 14 in the Electronics and Circuitry section where these parts are described in further detail)

Figure 10: A figure showing the cam section of the device with the helical cam, shaft, and motor

The follower includes a slider, which holds the rails. The slider is made up of four 3D printed linear bearing holders offset from the vertical base by raisers. The linear bearing holders keep the provided 8mm linear bearings in place and space the two 8mm rails at a predetermined distance to avoid binding. The rails are kept from sliding out of the bearing by 3D printed shaft collars. At the end of the rails are two 3D printed L shaped rail holders that each slot in a rail from the slider, as well as the two 8mm rails that the follower rail holder slides along. The rails are held in these slots by clamps which are built into these parts. By building the clamps into the parts, we are able to avoid the struggle that comes with press fitting the rails, while maintaining a firm hold on the rails. One of the rail holders is also designed to fit the pen brush, using a slot and 3D printed pen holder piece. Additionally, due to the weight of the final system, we added a spring that we could tune by changing the height of the attached shaft collar to minimize issues of slippage when the follower climbs a steep slope on the cam.

Sliding along the two rails are four 8mm linear bearings, 2 per rail, which are held inside of the upper portion of the follower rail holder. The upper rail holder is bolted to the lower follower rail holder, with a sponge-like double-sided tape placed between the two, to decrease unwanted motion. The lower part of the follower rail holder keeps in place the 6 mm rail holding the follower, and is designed to be rigid to reduce out of plane motion that would resulting in slippage. At the base of the rail is the follower, in contact with the cam, that consists of a wheel, a 3d printed wheel holder, and a metal dowel, which keeps the wheel and holder together.

Figure 11: A picture focusing on the follower portion of the device including the slider portion, the follower rail holder section, and the follower wheel

The final section in the assembly is the gear train and cylinder. This section is attached to the rest of the system by a belt and pulley system, where the pinion for the pulley is attached to the cam rail. A toothed belt connects the pinon to the gear which drives a 8mm rail. This rail is held up by two bearing holders, bolted to the base, containing 8mm ID ball bearings. At the end of the rail is a 1.7'' diameter, 20 tooth bevel gear with a 8mm inner diameter. This bevel gear meshes with a second bevel gear on a 8mm vertical rod holding the drawing cylinder, which contains four magnets that hold the paper in place and a fifth magnet that ensures that the ends of the paper meet. The cylinder is in line with the aforementioned pen slotting rail holder. The cylinder rail is connected to the frame by a bearing holder and plate, both of which hold a 8mm ID ball bearing and are bolted to the vertical and horizontal base respectively.

Figure 12: A picture showing the gear train and drawing cylinder

Electronics and Circuitry

Our electronics consist of a 12V power source, a stepper motor (17HS4401), a stepper motor driver (DRV8825), two push buttons and an Arduino Uno. The Arduino Uno houses the logic for controlling this circuitry. The two push buttons are for users to control the machine, one for drawing (spinning cam forward) and one for resetting (spinning cam backward). 

Figure 13 & 14 :  A depiction of the electronics of the device during design and testing and the electronics assembled having been fixed to the base with proper wire management in the final version of the device

Software

The control software programmed on Arduino is based on a state machine. For stepper motor control, we use a popular library, AccelStepper.